The present invention relates to a selective doping crystal growth method by which specific dopant atoms and/or specific molecules are introduced selectively into a desired region in growing a crystal by using molecular beams consisting of constituent elements and ion beams consisting of the dopant.
As the method for introducing specific atoms into a desired region of a crystal with, for example, the purpose of selectively doping the crystal with impurity atoms, it has been usual to provide a mask of photo-resist or metallic thin film on a surface of the crystal and to introduce the specific atoms by diffusion or ion implantation. In this method, however, the atoms are forced into the already grown crystal and thus it is not a method for introducing the specific atoms selectively into a desired region of a crystal during growth.
Therefore, in the above method there is a limitation on the doping depth of the atoms from the surface of the specimen and, according to this method, it is very difficult to obtain a crystal having a complicated doping profile which may, for example, be produced by forming a layer selectively including atoms with a pattern on another layer selectively including other atoms with another pattern.
In most of the conventional methods, a heat treatment is required which does not always favorably affect the crystalline quality thereof.
Further, a method of growing crystal with selective doping has been known in which the fact that ions have electric charges is utilized and the traveling directions of ions are controlled by using deflection electrodes so that portions of a substrate where the doping is required are irradiated with ions. This method is capable of selective doping during crystal growth to some extent. However, the method is not effective since it is difficult to accurately inject the substrate with heavy ions over a relatively wide area and in a desired pattern.
Further, in order to achieve the selective growth of crystal, a mask must be disposed in front of the substrate surface to selectively block ion beams, and thus there is a possibility of blocking molecular beams of constituent elements, making the crystal growth impossible.
As another conventional method, a molecular beam epitaxial method has been known in which a crystal is grown on a substrate surface by irradiating the substrate surface heated to a suitable temperature with molecular beams of constituent elements of the crystal. In this epitaxial method, the crystal is selectively grown by a suitable means such as a mask provided on the substrate surface.